Air flow control apparatus



March 20, 1951 w. E. WELCH AIRFLow CONTROL APPARATUS 2 Sheets-Sheet Filed Dec. 26, 1944 March 20, 1951 w. E. WELCH 2,545,563

AIRFLOW CONTROL APPARATUS Filed Dec. 26, 1944 2 Sheets-Sheeb 2 Fvg. z.

Patented Mar. 20, 1951 AIR FLOW CONTROL APPARATUS William Evert Welch, Minneapolis, Minn., Aassignor to Minneapolis-Honeywell Regulator Compa-ny, Minneapolis, Minn., a corporation of Delaware ApplicationDecember'Z, 1944, Serial No. 5695791 13 Claims.

The present invention relates to the pressuriz ing of an af' aft cabin. It has, been found .that a suitable source of air under pressure for ,prese surizing an aircraft cabin -is the turbo supercharging equipment of the aircraft power plant. The -air required for Ventilating and maintaining cabin pressure is but a small fraction of the air required for the aircraft engines, therefore air for the cabin can readily Ybe obtained by divert.- ing `a portion of the discharge from one or krmore superchargersinto said cabin.

By the use of a now limiting means in the conduit through which air is diverted from the superchargers into the cabin, the means for controlling cabin pressure -under some conditions, comprises Vmerely means for regulating the flow of air from the cabin. However, superchargers of a multi-engined airplane may be simultaneously regulated from a single control means .in a manner to maintain uni-form pressure boost and uniform engine power. If a low boost in pressure is needed for the engines, the discharge pressure of the superchargers may be -less than the pressure required vin the cabin. Under these circumstances, there may be 1no flow of air .into the cabin, ventilation stops, Vand pressure cannot be maintained, thus causing the cab-in pressure to drop below that required.

It is therefore a principal object of this invention to provide means 'for controlling vthe turbo superchargers of an aircraft according to `the Aair needs of the engines, but 'wherein the control of the super-charger or superchargers supplying cabin air may be'modied to automatically maintain at all times suicient discharge pressure to insure Va desired flow of air to the cabin.

It is an object of this invention to provide control means for adjustably establishing .a variable low limit of turbo supercharger discharge pressure enough above cabin pressure lto insure the desired airow to said cabin.

It is an additional object to provide simple, light, and compact apparatus for modifying an electrical control system for a plurality of turbo superchargers in a manner to insure desired discharge pressure.

It is also an object to provide means automatically divoroing the control of Van inboard engine supercharger from that of an Youtboard engine supercharger when added boost is required from said inboard engine supercharger to provide air under suitable pressure forthe cabin.

It is a further object of the invention to provide a control system for the superchargers of a multi-engined aircraft ywhereinsaid superchargers are controlled in response .to power demands, wherein at least one .of said superchargers is also controlled in :response to cabinair demands, and wher l manual adjustments aresimplied minimized.

These .other objects will become apparent the description of .the present invention proceeds.

In the drawings:

Figure l .shows a schematic arrangement of .the

sent Vcontrol .equipment as applied toa four engined aircraft.

Figure 2 is more specific .schematic showingl of .the present control equipment .as applied vto be noted, ,the .present system .of `airflow controlV modifies Athe .turbo boost control system in .a man ner to provide sucient air pressure for cabin' pressurizing and the least disturbance ,to the normal operation of the Vaircraft engines. The present cabin .boost control system .is more suitably applied .to multi-engined aircrait, but itis notedithat it maybe :used oneven a single engined aircraft if ,it ,be .desired to provide a low limit of turbo .supercharger operation which will foe vari.- aoie according to the cabin pressure maintained.

In Fig. lof the drawing, .cabin lil is shown ,in its normal relation to inboard engines ,2 and 13 and .outboard engines l and 4 oi `a four-.engined aircraft. :Engines l to 4 are fitted withsuperchargers .l..|, 2|, 3l Aand .4l .driven .by turbines 12, 22, 32, and 42, respectively. The A,speed Yof each turbine is ,controlled by controlling its Waste gate I9, 2,9, 39, or 49, this being done by apparatuses ,13, ,23, 3,3, Aand 4,3, respectively. It is noted vthat the respective auxiliary and control equipment A,of xeach :of the engines is similarly numbered with the exception that the rst numeral ofeach number corresponds to the number of the respective engine. rlhus, in describing the equipment associated with any one engine, the same description will )be pertinent to each of the other engines. keeping vin mind the systemV 3 of numbering. While the superchargers of inboard engines 2 and 3 also furnish air to the cabin, as will be explained, the basic turbo control equipment is the same except for the cabin boost control which will be further discussed.

To broadly illustrate the association of the present apparatus, it is noted that the super.- charger II of engine No. I delivers air through carburetor I4, which is provided with throttle lever I5, to the engine. Supercharger I| is driven by turbine I2 through shaft I6. rTurbine I2 is driven by the exhaust gases from engine No. I delivered to same through the exhaust pipe. The gases may pass through the turbine wheel or may pass through said turbine 'without generating power by exhausting past waste gate I9. When waste gate I9 is wide open, this constitutes the path of least resistance for said gases, hence only a negligible quantity of gas goes through the turbine in a manner to cause operation thereof. However, as waste gate I9 is closed, the increased now of gas through the turbine causes it to rotate at an increased speed. The speed of the turbine, and the discharge pressure of the supercharger are thus seen to depend on the adjusted position of the waste gate.

The position of waste gate I9 is determined by a reversible two-phase motor whose operation and direction of rotation is determined by the current supplied by amplifier |20. The current supplied by amplier |26, and the phase relation of same, is determined by the signal currents supplied said amplifier.

,The signals supplied amplier |20 are the result of a compound electrical network including turbo boost control |80 and control apparatus I3.

, It will be noted, disregarding cabin boost control 50, that turbo boost selector |80 simultaneously adjusts the operation of the turbo control apparatus of each engine. The turbo control system thus far described is similar to that disclosed in the copending application, Serial o. 48.67.992, of Hubert T. Sparrow et al., filed May 14, 1943, now Patent No. 2,466,282, issued April 5, 1949,1and reference is herein made to said patent for'famore complete description of the present system. In addition, the present system will be morefully explained as the specilication proceeds.

At this point, it is noted that means are provided for controlling the superchargers of the engines of a multi-engined aircraft and for simultaneously adjusting the supercharger dis charge pressure to be maintained by the control apparatus. The cabin boost control 50 has been disregarded during the preceding discussion, this being permissible for, under some conditions, said control may have no effect on the operation of the turbo control system.

In addition to supplying air to engines 2 and 3, superchargers 2| and 3| also supply air to cabin I0 through ducts 21 and 31, said ducts being provided with Venturi flow limiting means 28 and 38, respectively. Tube 5I connects cabin boost control 50 with the interior of cabin I0, tube 52 transmits the pressure existing upstream of flow limiting means 28 to controller 50, and tube 53 -is connected to 3`| upstream of 38 and to said controller 50.

' Cabin boost control 50 comprises means for increasing the signal strength to amplifiers 220 and 320 if the other apparatus does not call for suiiicient supercharger discharge pressure to satisfy-cabin air demands. As shown in Figure 1,

this device comprises minimum flow control adjusting means BI and 6I, signal lights 59' and 59 and switches 55' and 55, associated with the ycontrol of apparatuses 23 and 33, respectively.

In addition, a low altitude cruise transfer potentiometer having an radjusting means 56 is also provided. The operation of this control, as well as the rest of the apparatus, will be explained later. Further, as cabin -boost control 50 in. cludes the means by which the present invention is distinguished from the aforesaid Sparrow et al. application, this apparatus is more specifically shown in Figure 2 as is the basic turbo control system, each being shown associated with engine No. 3. Because the present invention is diiilcult to explain without referenceto the turbo boost control system, this too, will be more fully de-4 scribed. In describing the turbo boost control system, as specically shown in Fig. 2 and as related to engine No. 3, it should be noted that the description applies equally well to the apparatuses of engines I, 2 and 4. The present specic description is made of engine No. 3 and its associated apparatus rather than engine No. I because the turbo control apparatus is the same in either case, but the turbo supercharger of engine No. 3 also supplies cabin air under the control of control 50. In addition, it is noted that the association of the cabin boost control with the turbo boost control apparatus of engine No. 3 is the same as that with engine No. 2.

Supercharger 3| is driven by turbine 32 through shaft 33 and also imparts motion to shaft 38' by means of gearing. Turbine 32 is driven by exhaust gases from engine 3 and its speed is governed by permitting more or less of the exhaust gases to `pass out through a by-pass controlled by Waste gate 39. It was previously noted that the power output of the engines may be controlled by varying the discharge pressure of the superchargers, and it is again noted that the discharge pressure of said superchargers depends on the speed of rotation of their respective driv. The speed of rotation of the tur-YV bines depends on the amount and pressure of ing turbines.

the exhaust gases which pass through the blades of ,the turbine, this being regulated by regulating the flow of gases through the 'py-pass which isv controlled by the waste gate. It therefore be-l comes clear that turbo discharge pressure may be controlled by controlling the waste gate of the respective turbine. The position of waste gate 39 is controlled by reversible geared motor means 309 operating arm 30| of bell crank 32 which is connected by link 303 to arm 3634 which is at,

tached to the shaft which carries Waste gate 39. Angular motion or" arm 59| causes rotating movement of waste gate 39 and thus varies the quan-v tity of gas which may by--pass the turbine wheelv of turbine 32. In the position shown, waste gate 39 is in wide open position. A counterclockwise A movement of arm 39| willcause closing movement of waste gate 39 and thereby increase the speed of the turbine 32.

As before noted, geared motor 309, which drives.

energized from current supplied by amplier means 320 through wires `|52 and |63 leading,

5. from terminals 32| and 322, respectively. The direction of rotation of the motor depends upon the phase relation of the current supplied from the amplifier. If the current supplied by the amplifier leads the current supplied by the line, rotation will be in one direction whereas, if the amplier supplies current lagging that supplied by the lines, rotation will be in the opposite direction. In the practical embodiment of the present invention, motor 309 also includes a follow-up, or rebalancing, potentiometer 330. However, for the purpose of this schematic showing, the rebalancing potentiometer is show-nas a separate element operated by arm 395 of bell crank 3.02.

, Amplifier 326 has signal input terminals 323 and 324. It also has output signal terminals 38| and 322, as Well as power supply terminals 325 and 326. This amplifier is of the sort which amplifies alternating current signals and maintains .i

their phase relation. Any suitable ainpliner that will maintain the same phase relation through same may be used, but I prefer to use one such as shown in the copending application of Albert P. Upton, Serial No. 437,561, led April 3, 3.942, now Patent No. 2,423,534, issued July 8, 194.7. Power for the operation or" amplifier 326 is supplied by the circuit: line |58, wire terminal 325, terminal 326, wire |52, and line |53. Line 50 is a common and grounded wire of the airplanes power supply whereas line |53 is the hot wire and, ordinarily, is energized with a 115 volt, 4Q@ cycie alternating current. The airplane power supply also includes line |60, which for its return uses common wire |50, and which is energized with a 26 volt, 400 cycle alternating current.

Amplier 329 receives signals from a compound network comprising a plurality of electrical networks connected in series. The input signal circuit of amplifier 320 is traced from terminal 323 through wire 321, arm 33| of follow-up potentiometer 330, electrical network 349, arm of velocity responsive means 342, wire 343, arm of acceleration responsive means 345, network 360, arm 36| of induction pressure responsive means 362, wire 363, terminal of cabin boost control means 50, wire 1|, arm 12, resistor wire 14, terminal 15, wire 334, and turbo boost selector |80. Turbo boost selector |80 is grounded through arm |8| and wire |82 and receives current through wires |99 and |9| from lines and |53, respectively. Input terminal 324 of amplifier 329 is connected by wire 38|! and wire 38| to grounded wire |82. Arm 33| of follow-up potentiometer 330 is actuated by arm 338 attached thereto and connected to arm 335 of motor 300 by link 339.

Network 340 comprises a transformer 345 having a primary winding 341 energized through wires 348 and 349 from line wires |53 and |59, respectively. Transformer 346 includes secondaries 350 and 366. Resistor 356 is connected to the left hand terminal of secondary 350 wire 352 and connected to an intermediate tap 354 by wire 353. Resistor 351 of follow-up potentiometer 336 is connected to tap 355 by wire 358 and to the right hand terminal of secondary 350 by wire 359.

Velocity responsive means 342 and the acceleration responsive means 345 are driven by a common shaft 36', a continuation of shaft 36 shown in the upper portion of Figure 2. Any suitable velocity responsive means and acceleration responsive means may be used in the present instance, but I prefer to use a combined structure such as disclosed in the application of Hubert T. Sparrow et al., Serial No. 476,798, filed February 22, 1943, now Patent No. 2,474,203, issued.

June 2l, 1949. Arm 34| of velocity responsive means 342 moves to the left across resistor 355 in the event of overspeed of the turbine 32.

Electrical network 360 is seen to comprise a bridge circuit having an input source of current from secondary 366 of transformer 346. The left end of said secondary is connected to said network by wire which connects to wire 368, non-resistive slide portion 369, resistor 318, wire 31|, and wire 31'2 to the right end of said secondary. Wire 351 also connects to wire resistor 314, and wire 315 which connects to wire 312. Arm 344 of acceleration responsive means 345 is moved to the right across the non-resistive slide portion 389 and resistor 318 as acceleration is increased. Because the iirst portion of travel of arm 344 is on non-resistive slide portion 369,.

there is no response or change in circuit conditions for relatively minor accelerations of the turbine.

Induction pressure responsive means 382 operates arm 36| over resistor 314 to the left as induction pressures rise. Device 332 comprises an evacuated bellows 311 extended by spring means and coacting with arm 35| in opposition to bellows 318 connected by tube 319, to the discharge conduit of supercharger 3|.

rfurbo boost selector network |39 comprises a transformer |88 having a primary |83 connected to lines |53 and |53 by wires |98 and |9|, respectively. The left end of secondary |92 of said transformer |88 is connected by wire |93 to the left end of resistor |94 while the right end of said resistor |94 is connected to the right end of said transformer by wire |95. Wire |95 also connects to the right end of secondary |92, and wire |91 is connected to an intermediate tap |88 of said secondary. Calibrating potentiometers |83, 283, 393, and 483 are connected between said wires |96 and |91. Arm |8|, which moves across resistor 94, is manually controlled by knob and is used to establish the desired boost for the turbo superchargers of the aircraft. As will be made clear later, with the exception of the adjustment permitted by Calibrating potentiometers, adjustment of operation of the outboard superohargers is manually adjusted only by arm |8| moved by knob |85. As will be seen, operation of the turbo superchargers of the inboard motor shown is subject not only to turbo boost selector |80, but also to regulation by cabin boost control 50, to be described.

Cabin boost control means 53 comprises differential pressure responsive means 62 which includes bellows 33, connected to the interior of the cabin by tube 5|, and bellows 64 connected to the upstream side or Venturi means 35 and by tube 53. Bellows 53 and 64 coact with pivoted lever 85, which is urged to the right by adjustable spring means 56. Spring means 66 is tightened by clockwise movement of adjusting knob 9|. Pivoted arm 65 includes contact portions which engage stationary contacts 83- or 8|, contact 8| being engaged when cabin pressure is relatively high as compared to the supercharger discharge pressure. Arm 65 is connected by wire 92 to switch terminal 83 which is engageable by manually movable switch means 55.

Differential pressure responsive means 62 and manual switch 55 control the operation of a two-phase resistor type reversible motor 35. Motor 85 comprises an armature 86 and field windings 81 and 88 arranged 9G electrical degrees apart. Winding 81 is energized by the circuit: line |50, wire 90, terminal 9|, wire 92, wire 33, winding 81, resistor 9d, wire 95, terminal 96, and line |60. Winding 83 is energized by the circuit: line |50, wire 9i), terminal 5|, wire 92, wire 93, winding S3, wire 91, resistor 99, wire |59, Wire t5, terminal 96, and line |652. With the circuit as -recited, it is noted that the windings are equally excited and that an equal amount of resistance is in circuit with each one, resistors 555 and 59 being of equal value. These conditions are not conducive to rotation of said armature; in fact, the armature is magnetically locked in place.

In addition to the circuit above described, other wiring is associated with said motor. A short circuit vmay be established around resistor Sii by the circuit.: wire lili, switch blade H32, switch blade ill-i5, wire |65, and wire |55 to terminal |01 which is engaged by manual switch 55. Manual switch 55 connects by wire Hi8 to resistor SQ.. Itis thus noted that when switch 55 engages terminal 51 and when switch blade |52 Vis vin engagement with switch blade |3, a short circuit is established around resistor g. Switch blade |53 has an extension portion lull through which blade |03 is operated in a manner to be described.

When swit s. blade is in contact with terminal 83, an ther circuit short circuiting resistor 9B may be established by the wire itl, switch blade m2, switch blade |633, wire IE5, wire Iil, switch contact 88, arm E5 of diierential responsive means :82, wire 82, terminal S3, switch blade 55, and wire Hi8 to resistor t. However', blade B5 is not in engagement with contact 38, hence 'this circuit cannot be considered complete.

Resistor SQ may be shortncircuited by the circuit: wire i i, switch blade l I2, switch blade vE i3, wire H5, switch contact Si, arm t5, wire 82, contact $3, switch 'blade 55, wire itil, wire ill, and resistor E9. Switch blade H3 has an extension |l1l useful in a to be described. It is noted that only when switch blade 55 contacts terminal 83 can resistor t@ be short-circuited. Short-circuiting `one or the other vof said resistors alters the phase relation of one of the windings of motor relative to the other and causes rotation, the direction of rotation depending on which ci the resistors in short-circuited.

Armature til of motor 85 drives arm 'i'through gearbox hiss to the rigt or left across resistor 13 depending the rotation ci said armature. Arm 12 includes Astop portions ii'l and fi i8 which may coact respectively with extended switch portions ll-'l or iid. In the position shown, stop portion H1 has engaged portion l and broken Contact between switch blade ylilil .and blade |32 thereby opening Vthe short-circuit which would other-,vise exist around resistor 9d. The Acircuit which might by-pass resistor 9S is also opened because switch 'blade 55 is in contact with terminal 01 instead of terminal S3. Thus, armature 85 is now magnetically locked place but rotation may be caused in a direction to move arm 12 to the right if switch blade 55 be moved to engagement with contact 53. When stop portion H8 of arm F12 engages .extension portions Il@ of switch 'blade H3 and breaks contact between switch blade l i3 and clade l i2, contact is `made between switch blade H3 and switch blade |28 which energizes signal llight 55 :by the circuit.: line IEE, wire 99, terminal 3l., wire g2, wire 52%., light 59, wire vl22, `switch blade |29, switch blade H3, wire H5, Contact El, blade 55, wire 32, switch contact 83, switch arm 55, lwire lila, wire 95, terminal V96, and line l. Thus light 59 may be energized when blade 'l2 is moved to the extreme: right of resistor 13. V1

In addition to reset resistor 13., cabin boost control 5S also includes low altitude cruise transfer means 51 which is adjusted by manual knob wire |82 to ground. An arm |4| is adjustedacross resistor |35 by knob 55'.

As Figure 2 shows only the control equipment needed for the No. 3 engine of the aircraft .and the equipment common to the control apparatus of the other engines, of the aircraft, it should be noted that in this gure portions o1 cabin vboost control 5E! would normally be duplicated. As

shown in Figure l, cabin boost control 5i) would,v

if both inboard engines of the aircraft are used for pressurizing the cabin, comprise another pressure responsive means similar to 52, another motor such as S5 complete with its control equip-'- nient and wiring, an additional signal light means, and a reset potentiometer such as that in# cluding arm 'i2 and resistor 13. The lowaltitude cruise transfer means 51 is common to the control nieans for both sides of the plane. Arm 1M is connected to the right end of resistor 13 tby wire |132, and wire |43 is shown leading tothe right end of a duplicate resistor` which would be used in the dual controller. Likewise, cabin pressure is transmitted to cabin boost controller 5E 'by' tube 5| which leads into a T riitting, one end ofi which extends into bellows 63 and the other end ,of which is shown plugged. This plugged endwould nornally extend to the cabin pressure -re' sponsive bellows of the duplicate differential pressure responsive means.

While certain of the present apparatus hasbeen rather specically described, it is obvious that many changes may be made within the scope of this invention. For instance, motor S5 may be any conventional reversible motor; `differential pressure responsive means @2 is subject to many modications, and the differential pressure may be obtained from the inlet and the throat of the venturi instead of from the inlet and the cabi-n as shown. In addition, the present cabin boost control is shown associated with a turbo boostl control system such as fully disclosed in the'` aforo-mentioned Sparrow et al. Patent 2,466,282

and, while said turbo boost control system is thatY preferred, the present cabin boost control system may be used to establish a low limit of turbo operation for any suitable turbo boost control system.

To more fully explain the correlation of the present control apparatus, the following descrip-Av tion oi" operation follows.

Operation In considering the operation of the present control apparatus, it is noted, as before pointed out, that the various elements of the apparatus,

are in their positions of rest, with the airplane stationary vand at sea level. The turbo boost selector |85 ,is adjusted to zero boost, the induction pressure Vresponsive device 352 indicates atmospheric pressure, the acceleration responsive means 345 is in a position of no acceleration, the velocity responsive means 342 shows zero velocity, and waste gate 39 is wide open. Further, the switch of the cabin boost control means is in off position and arm 12 is at a position to add no voltage to the turbo boost control system.

As before noted, operation of waste gate motor 360 depends upon whether or not its amplifier 320 is furnishing current to same. Further, the direction of operation of said motor depends upon the phase relation of the current supplied the motor by the amplifier as compared to that of the line current. Since the phase relation of the output of the amplifier depends upon that of the input, an analysis of the control networks will determine whether or not a signal is being supplied said amplifier and the phase relation of same. To expedite a consideration of these networks, the instantaneous current relation existing in the network during a half cycle may be considered. Then, the left end of each of the bridges may be considered negative in potential and the right end positive. Considering the operation of the network on a half cycle basis, it

may be determined whether or not there is a signal resulting from same and the signal will then appear to be either positive or negative in potential. However. with alternating current, a signal which is negative in potential at one instant becomes, a half cycle later, positive in potential. It is thus obvious that what appear to be positive and negative signals actually represent signals 180 different in phase. Therefore, while it is noted that signals of one phase relation will cause the waste gate motor to operate in one direction, and signals of another phase relation will cause said motor to operate in the opposite direction, in this analysis signals having a positive potential will cause the waste gate motor to operate toward open position and signals having a negative potential will cause said Waste gate to be closed. The voltage at arm |8| of turbo boost selector |60, is shown to be zero whereas the potential at arm 365 of calibrator potentiometer 383 may be assumed as 26 volts above the left side of the network. Therefore, the signal from turbo boost selector |80 is 26 volts positive. With a 30 volt potential existing across the input terminals of network 360, arm 36| appears to be at a position corresponding to a potential of about 10 volts. However, arm 344, being at the left end of resistor 316, is at zero volts. Therefore, the output current from network 360 would be negative 10 volts. Arm 34| is at the extreme right of resistor 356, the potential between wires 353 and 358 may be considered 6 volts and, since arm 33| is at the left end of resistor 351, then arm 33| is thus ony 6 volts higher in potential than arm 34|, therefore the output of network 340 is G volts positive. Adding up the voltage signals from each of the networks, it becomes apparent that there exists a signal of 22 volts positive, therefore waste gate motor 300 maintains said waste gate wide open, further rotation being prevented by internal stops associated with said motor.

Assume now that the aircraft is being prepared for the take-off. As the power output of the engines is increased preparatory to the beginning of the flight, it is obvious that the added rate of air flow through the induction system will cause the induction pressure to drop. As will be noted, as arm 36| moves to the right,

344 becomes more negative relative there- 1D to; however, as the total travel of arm 36| to the right from its previous position permits a change of only 20 volts, this in itself cannot cause operation of the waste gate motor. For the take-off of the aircraft, a high power output is ordinarily required from the engines, so let it now be assumed that arm i8! is moved to position 8 on resistor |94 of turbo boost selector |86. Position 8 corresponds to a potential of about 24 volts positive relative to the left side of the network and, as arm 355 is at a potential of about 26 volts positive, relative to said side, the output of the turbo boost selector becomes two volts positive. In the meantime, due to the high rate of air ow through the induction system, and the result of pressure drop therein, assume that arm 36| has moved to the mid-point of resistor 314. Arm 344 is then l5 voits negative with respect to arm 36|, thus the output of network 366 is 15 volts negative. Arm 34| may be considered to remain in its previous position as may arm 33|. With this assumption, the output of network 340 is again 6 volts positive. However, on adding the voltages, it becomes apparent that the output of the series of networks is a '7 volt negative signal. As the negative signals will cause a closing movement of the waste gate motor, arm 33| will be moved to the right across resistor 351 and thus increase the positive potential of network 340 sufficiently to offset the negative voltage signals of the previous networks. This would appear to require movement of arm 33| across 1-"f`of said resistor assuming a 12 volt potential existing across resistor 351. Thus, the waste gate would then be moved more than half closed. However, as the waste gate moves toward closed position, the induction pressure rises, therefore the negative voltage signal of network 360 is diminished as arm 36| is moved to the left across resistor 314 by the rising induction pressure. Rebalancing is thus effected not only by the follow-up potentiometer of the waste gate motor, but also by the induction pressure responsive means. It has been assumed up to this point that the rate of acceleration has been within due limits and that the velocity of the turbine has not exceeded its proper bounds. As before noted, portion 369 of resistance 310 represents a slide portion of negligible resistance change, therefore minor changes in acceleration have no eifect on the network. However, should the acceleration become excessive, arm 344 is moved to the right across resistor 310 and, as it approaches the position of arm 36| or travels to the right thereof, it tends to wipe out the negative signal and to cause a positive signal thereby tending to drive vthe waste gate motor open. Driving the waste gate open causes a reduction in turbine speed and therefore tends to limit the acceleration of same. In the same manner, if the velocity of the turbine reaches excessive values, arm 34| is moved to the left across resistor 356 and thus is moved further to the left of arm 33|, thereby causing positive signal voltages of increased magnitude which tend to open the waste gate. The present description of operation of a turbo boost control system, shown specifically for inboard motor No. 3, applies in the same manner to each of the motors of the aircraft. Thus, when the switches of the cabin boost control are turned to off the turbo superchargers of each of the engines of the aircraft may be simultaneously controlled by the turbo boost selector in the manner described.

and switch 55 may be thrown to the vlative. 'and arm 33! ,-"f of the way across 351, the out- 'Volts positive.

ythe cabin under the required pressure. 'necessary that the air supply beat a pressure "sufficiently higher than cabin pressure-to give a` desired rate of flow, it may be assumed that theV For a more complete and detailed description lof the operation of this turbo boost control sysljtem, reference is again made to said Sparrow et al. Patent No. 2,466,282.

' With the control knob of the turbo boost selector turned to position 8, and the aircraft "rising, attention may now be directed to the ycabin boost control.

The pressure to be maintained in the cabin, as before mentioned, is normally controlled by pressure regulating means, ,not shown, which controls the flow of air from the cabin. Assume that a cabin pressure of 22 inches of mercury is to be maintained, this pressure corresponding to an altitude of about 8,000

feet; this pressure being generally considered 'about as low as human beings normally should stand. The minimum flow control knob may be adiusted to a position of medium flow, 'knob 56 of the low altitude cruise transformer potentiometer may be adjusted to its 8000 foot mark automatic position.

With a turbo boost adjustment at position 8, it is noted that the turbo superchargers are ooerating to provide a relatively high induction pressure. This pressure may be considered to be well above the 22 inches of mercury cabin pres- 'sure being maintained, so arm 65 of diierential lpressure controller 62 is moved to the left into engagement with contact 80. With arm 65 in engagementv with contact 80, and switch 55 engaging contact 83, motor 85 remains in the position shown and there is'no change in operation of the turbo boost system. Ifl the airplane now levels off for cruising at about a 10.000 foot elevation, high power outputs may no longer be demanded and the turbo boost selector may be turned back to about position 5, or lower. With 'arm 8| at position 5, the signal output of network |80 1's 11 volts positive. Assuming that arm '36| is at about the :mid-point of resistor 314, and arm 344 is at the left end of resistor 318, the

output of network 360 is again about volts neg- With arm 34| at the right of resistor 356 put of network 340 is 13 volts positive. n Adding these voltages reveals that there is a signal of 9 As positive voltage signals cause opening of the waste gate, the waste gate is now :driven toward open position and arm 33| moves lto the left across resistor 351.

In addition, as the waste gate'is opened, the induction pressure diminishes and may be considered to drop to about inches of mercury. With an induction lpressure of about 20 inches of mercury, the voltl vage output of network 360 may become about 22 volts negative. Assuming that there is no overspeed, it then becomes apparent that the output Thus, it is noted Obviously, the discharge pressure gines must be increased if air is to be supplied to As it is tend to rise.

higher than cabin pressure to give the desired rate of air ow through restrictor means 38. Thus, if the diierential of pressure between cabin and turbo discharge is less than 2 inches of mercury, arm 65 makes engagement with contact 8|. If the differential pressure exceeds 3 inches of mercury, for instance, arm 65 engages contact 86, and at intermediate differential pressures, arm 65 engages neither of contacts 80 nor 8|. With switch 55 in automatic position .(engaging contact 83), and the diierential of turbo discharge pressure over cabin pressure less than 2 inches of mercury, arm 65 is in engagement with contact 8l, resistor 99 is short circuited out of the motor circuit and armature 86 of motor 85 is rotated in a direction to drive arm 12 to the right across resistor 13. Movement of arm 12 to the right across resistor 13 adds negative voltage signals to the turbo boost control network and thus tends to cause closing movement Yof waste gate 39. Closing movement of waste gate 39 will then cause a rise in induction pressure and an increase in the dierential of pressure between turbo discharge vand cabin pressure. Arm 12 is geared to be moved slowly by armature 86 so lthat the readjustment ofthe turbo boost con'- trol system takes place no more rapidly than the differential of induction pressure to cabin pres'- sure varies, this being required to keep the system reasonably stable. If the desired differential of turbo discharge pressurel to cabin pressure rises above the required 2 inches of mercury when arm 12 is but half way across resistor '.13, arm 65 is moved out of engagement with-contact 8| and motor l85 is stopped. Arm 12 therefore remains in its half wayrposition on resistor`13. Should the differential pressure diminish, arm

'B5 would then be reengaged with contact 8! and arm 12 would again move to the right across resistor 13. However, should the diierential vrise above the aforesaid 3 inches of mercury, arm 65 vwould engage contact 80 and drive motor 85 in a reverse direction, thereby moving arm 12 to the left across resistor 13 and diminishing the negative voltage signal applied to the turbo boost system. This would tend to again open waste gate 39. It is thus noted that the cabin boost control system will add voltage signals to a turbo boost control system only sufcient to cause a turbo boost discharge pressure to rise to the required level to give needed cabin ventilation. Obviously, as the turbo discharge pressure of the inboard engine is raised by the cabin boost control, the power output of said engine will also To maintain best control of the airplane, it is required that al1 of the engines be operated at approximately uniform poweroutput, therefore to offset the added boost pressure of the inboard engine, throttle must thereby be operated to restrict the power output of the inboard engine to the same level as the other engines. Of course, if cabin boost control also controls No. 2 engine, its throttle must likewise be adjusted. y

It is noted that the cabin may be ventilated without the use of a cabin boost control by keepjing the turbo boost control selector adjusted to a position of about '1 or higher at all times and then, if lower output of the engines be desired, -the lower output may be vobtained by closing the throttles of said engines. However, this scheme of operation is inferior to the present described system in that added manual manipulation of -throttles' is required, -difcultymay be lhad in .eter is thereby decreased. potential across secondary 134 isr 12 volts, and

adjusting the turbo discharge pressure to exactly `thev point required to give the desired ventilation 'Without overshooting the minimum desired diiferential, the eiciencies of all of the engines are lowered due to the operation under partial throttle. It is noted that the erliciencies of the inboard engine or engines with the present cabin boost control system in operation are somewhat lowered because of a throttled operation required for same, but because the outboard engines are not'r affected thereby, their cfliciencies remain high. Further, the interference with the eiiin ciencies of the inboard engines is a minimum because the present cabin boost control automatically calls for only sulncient boost to give the required flou' of air into the cabin. In addition, it" has been found that under some conditions, the properly controlled diverting of air from the inboard engine superchargers contributes to smooth operation of said engines. Under light loads, there tends to be sur. 'ng in the induction systems whichcauses un table running or" the respective engines. By diverting a portion of the air from. a supercharger to the cabin, surging is minimized and smoother engine operation results. by setting the control knob to the desired point, the system automatically compensates for diierences in ruiming conditions, etc., and provides the needed pressure for the cabin.

The present cabin boost control meansv is of value'when the airplane starts descending toward a landing neld. Then the cabin pressure may be increased at a predetermined rate by the pressure regulating means but it is noted that the pressure regulating means is dependent on, and proper ventilation requires, the maintenance oi a proper air non" into the cabin. As the engines are usually adiusted to low power outputs when descending, it is obvious that correction must be applied to the inboard engines control system to maintain the pro er air now. Further, an eiTort may be made to build up the cabin pressure to that of the neld at which the landing is to be made prior to landing so that the cabin boost control can be Witched to orf position just before landing. Then, ii an emergency take-off becomes necessary, the turbo boost control will have full authority. Without waiting ior motor 35 to readgust arm i2.

Because is advisable to warn the pilot when the cabin boost control adding all the voltage it can to the turbo boost control system to give the desired W, it is noted that when, arm 12 reaches the e; erneright oi its travel, stop por-i tion H3 engages H4 and mot-es switch arm H3 out of engage lent With arm H2 to prevent iurther travel ci the motor which would tend to drive arm 'l2 the end of resistor 73. This also drives said switch arm l .'3 into engagement with switch arm les thus causing energization of signal light 5S. The energizing of signal light 59 indicates to the pilot that the cabin boost control can add no more voltage to the turbo boost system unless knob 5e be adjusted.

The am unt of voltage that may be added by movement of arm 'i2 across resistor 'i3 is determined by the low altitude cruise transfer potentiometer 51, and the voltage drop across said resistor is jointly due to the voltage added by potentiometer 5? the adjustment oi selector ISD. As the output voltage of selector i8!) is decreased, the potential drop across i3 is diminished and the sensitivity of the reset potentiom- Assurning that the that resistor |31 has half the resistance value o1' resistor i3d, it appears that the voltage at terminal 132 is about 4 volts and the voltage at the extreme right of resistor |35 is about l2 volts. Thus, by adjustment oi knob 5S, the voltage that may be added by operation of arm T2 across resistor 13' will vary ironie volts to 12 volts depending upon the position of, arm lai relative to resistor 35. In the position sh wn, with arm I4! at the 4 volt position, the total voltage that can be added to the turbo boost system when arm 'l2 is at the right of resistor I3 is e volts. When arm lill is adjusted by turning 56 until said arm is at the right oi resistor L35, then, When arm 'I2 is at the right of resistor i3, 12 volts may be added tothe turbo boost system. It has been found that an increase in signal strength of about 4 volts is all that is needed to give the desired supercharger boost for a cabin pressure of 22 inches of mercury, c rmonding to about eight thousand feet elevation. 'I ',vevcr, at times it is required that the cabin pressure be higher than 22 inches of mercury during the periods of comparatively loiv power output the engine, such as low altitude cruising. To be able to give the desired boost, loW altitude cruise transfer potentiometer 5l is adjusted by turning knob 56 to approximately the altitude to be maintained in the cabin, such as near sea level for very loW altitude dying. Then, operation of the dinerential pressure controller, made eiiective through movement of arm 'i2 across resistor '13, Will permit an additional l2 volts negative to be applied to the turbo boostr control. systemV to raise the discharge pressure sufdciently to insure cabin ventilation. It is thus noted that motor 85 driving arm 'i2 across resistor 'I3 in response to the operation of diiierential controller d2 determines Whether or not correction will be made, and the reative amount of cor ection that may be made, to the turbo boost control system to give the desired now oi air into the aircraft cabin. The low altitude cruise transfer potentiometer determines the relative authority of the cabin boost flow control, it being noted that the higher' the voltage applied to resistor i3 low altitude cruise transfer potentiometer 5l, the more authority the cabin boost control will have in modifying the turbo boost control system.

Ii the lov/ altitude cruise transfer potentiometer 5l should be adjusted for maximum authority, that is at its maximum voltage, and only a 22 inch cabin is desired, the apparatus will iunction as before, but with added sensitivity. Because movement of arm 'I2 across resistor 'i3 may involve a greater potential change than when said potentiometer is adjusted to minimum voltage, it will be noted that less movement will be required to increase the turbo boost pressure a given amount than When same is adjusted for normal operation with an 8G00 foot cabin although it is noted that adjusting arm ISI of selector to the right may oiiset any change in sensitivity to movement of arm T2 caused by increased voltage from potentiometer 5l. Added sensitivity is of no particular disadvantage excepting that the apparatus may become oversensitive and result in hunting.

It is noted that the pr1sent system comprises means adding voltage signals to an electrical turbo boost control system in response to the action of a diiierential pressure controller but it should be noted that many substitutions and equivalents suggest themselves upon a study of this system as before noted. In addition to the possible changes previously mentioned, it is contemplated that the low altitude cruise transfer potentiometer may be elminated by judicially selecting a voltage to be applied to resistor 'I3 which will not cause oversensitive operation o the apparatus and yet Will provide suiiicient modication of the turbo boost control system to give a desired air iiow under any practical operating condition of the aircraft.

In view of the many modications and substitutions that may be made in the present apparatus, the scope of the invention should be determined only by the appended claims.

I claim as my invention:

1. In an aircraft having a plurality of engines and a supercharged cabin, individual turbo sur perchargers driven by the respective engines with which they are associated for supplying air thereto, each or said turbo superchargers having a'controllable exhaust discharge means and an air discharge means, 'a Waste gate means controlling the iow of exhaust gas through said exhaust discharge means, conduit means for diverting air from one of said turbo supercharger air dischargel mLans to said cabin; an electric motor means for operating each of said Waste gate means, circuit means controlling each oi said motors, manually adjustable means for simultaneously adjusting said circuit means to thus simultaneously adjust the air discharge pressure of each of said turbo superchargers; and control means for supplementing the circuit means regulating the air discharge pressurel of said one supercharger comprisirry means responsive to air flow through said conduit means, switching means actuated by said air iiovv responsive means, ,reversible motor means controlled by said switching means, and impedance means in said circuit means adjustable by said reversible motor means in a manner to control said one turbo supercharger in a manner to maintain said air flow above a predetermined value.

2. In an aircraft having a pressurized enclosure, an internal combustion engine equipped with a turbo supercharger for supplying air thereto, said supercharger also supplying air to said enclosure, rst electrical circuit means for controlling said turbo supercharger in a manner to satisfy the demands of the engine, and supplementary electrical circuit means connected to said rst circuit means and including means responsive to the rate of flow or" air to said enclosure, said supplementary circuit means controlling said iirst circuit means in a manner to establish an adjustable low limit of operation of said turbo supercharger.

3. In a control apparatus for modifying a control system including an electrical circuit which "governs the operation of the turbo superchargers of a plural engined aircraft having a pressurized cabin wherein a portion of the air compressed by at least one of the superchargers is directed into the cabin, comprising, in combination, switch means, means responsive to the rate of air flow to said cabin for operating said switch means, a reversible motor means controlled by said switch means, potentiometer means including a resistor connected into said electrical circuit, said reversible motor means being connected to said potentiometer for adjusting the same, and manually adjustable means for varying the controlling eifect of said potentiometer.

4. In a control apparatus for modifying a control .systemlincluding anv electrical circuit which governs the operation of the turbo superchargers of a plural engined aircraft having a pressurized cabin wherein a portion of the-air compressed Aby at least one of the superchargers is directed into the cabin, comprising, in combination, diiferential pressure responsive ans adapted to be connected in a manner to indicate air now into said cabin, reversible motor means, means actuated by said differential pressure responsive means for controlling the operation of said motor means, variable impedance means adjustable by said motor means and provided with connection means for connection into the electrical circuit o1" said control systim, and connection means for connecting a source of electrical potentia across said impedance means. Y

5. In an aircraft having plural engines each equipped with and supplied air under pressure by a turbo supercharger, said aircraft having a pressurized enclosure, means for diverting -air from one ci said turbo superchargers to said enclosure, the discharge pressure of each of -said turbo superchargers being controlled by means including an electrical network, manual means for simultaneously adjusting each of said networks to vary the operation of all of the turbo superchargers substantially uniformly, circuit controlling means responsive to the flow of said diverted air, and means for connecting said vcircuit controlling means into the network of said one turbo supercharger in a manner to establish a low limit o discharge pressure for said one turbo supercharger even though said manual controlv may adjust another supercharger to a lower discharge pressure. Y f

6. In an aircraft having a plurality of engines and an enclosure maintained at a pressure above atmospheric, each of said engines being provided with a turbo supercharger, conduit means connecting the discharge of one of said superchargers to said enclosure for supplying air to said enclosure under pressure, means responsive to the flow of air through said conduit means, individual motor means for regulating the operation of each of said turbo superchargers, manually controlled electric circuit means for simultaneously controlling said motors for regulating the discharge pressures of said superchargers, and circuit controlling means governed by said air` flow responsive means connected into the circuit means controlling said one supercharger in a manner to increase its discharge pressure Without affecting the operation of the other superchargers. Y

7. In an aircraft having a pressurized enclosure, engine driven turbo supercharger means having air discharge means, conduit means connecting said discharge means and said enclosure, means responsive tojair oiv through said conduit means, reversible` motor means for controlling the operation of said turbo supercharger means, an electrical network circuit means for controlling the operation of said motor means, said network means comprising means provid,- ing signals varying in voltage andphase, signals of one VAphase causing operation of said motor means in a directionto raise the discharge pressure of the supercharger and signals of a dif,- ferent phase causing operation of said motor means in a manner to lower said pressure, the voltage of said signals determining the amount of movement of said motor means required to rebalance the network, yand means regulated by said means responsive to air now through said lconduit for introducing in said networksignals 17 of such phase and voltage as to cause a change in said discharge pressure.

8. In an aircraft having a supercharged cabin, means for controlling the pressure within said cabin, an engine driven turbo snpercharger means for supplying air to said cabin, first means responsive to a condition aecting the operation of said engin@ for controlling the operation of said turbo smercharger means, means responsive to the differential of pressure between the cabin pressure and the discharge pressure ci said supercharger, and second controlling means actuated by said differential pressure responsive means for modifying said first controlling means to maintain said differential pressure above a predetermined value.

9. In an aircraft having a supercharged cabin, means for controlling the pressure within said cabin, an engine driven supercharger means, conduit means connecting the discharge of said supercharger to said cabin to permit air flow therethrough, means responsive to the air flow through said conduit means, first means responsive to a condition affecting the operation or" said engine for controlling said supercharger means, and second control means regulated by said aii` flow responsive means for modifying said first controlling means in such manner that said air flow will be maintained above a predetermined value.

10. In an aircraft having an internal combustion engine equipped with a turbo supercharger, said supercharger having a waste gate, means for controlling the waste gate of said turbo supercharger for insuring proper air supply to said engine comprising an electric motor connected in operative relation to said gate, amplifier means for supplying current to said motor, rebalancing means driven by said motor, and electrical network including said rebalancing means for supplying signals of varying voltage and phase to said amplifier means in a manner to cause said Waste gate to assume a position to give the desired air supply to said engine, the operation of said gate by said motor being accompanied by operation of said rebalancing means in a manner to cause a cessation of said signals, means diverting a portion of the air from said supercharger t other useful purposes, and means responsive to said diverted air now and associated with said network for modifying the signals supplied amplifier in a manner to insure a predetermined minimum operation of said turbo supercharger even though the engine requirements for air are satisfied.

11. In an aircraft driven by an internal combustion engine, supercharger means driven by said engine for supplying air thereto, said aircraft having a pressurized enclosure, conduit means for diverting a portion of the air from said supercharger to said enclosure, electrical control means for regulating the operation of said supercharger including manually adjustable pressure selector means, said selector means previding an output electrical control signal of variable potential, means responsive to air flow through said conduit, and a potentiometer having a slider and a resistor and arranged to be adjusted in response to said air flow responsive means, said resistor being connected in series with said selector means, and said slider being 18 connected to said electrical control means for modifying the control of said supercharger in response to the air now to said enclosure.

12. In an aircraft driven by an internal combustion engine, supereharger means driven by said e'-gine for supplying air thereto, said aircraft having a pressurized enclosure, conduit means for diverting a portion of the air from supercharger to said enclosure, electrical control means for regulating the operation of said supercharger including manually adjustable pressure selector means, said selector means proan output electrical control signal of variable potential, means responsive to air flow through said conduit, and a potentiometer havintr a slider and a resistor and arranged to be adjusted in response to said air flow responsive means, said resistor being connected to said selector means, and said slider being connected to said electrical control means, and an additional adjustable source of electrical potential connected to said resistor in such a manner that the potential drop across said resistor may be varied in response to the adjustment of said pressure selector and said adjustable source.

13. In an aircraft having a power plant for propulsion which requires a supply of air under pressure, said aircraft also having a supercharged enclosure requiring a much smaller supply of air under pressure, means for supplying said power plant with air under variable pressure, first means including means responsive to said supply pressure for controlling the power output of said power plant by controlling said supply means, conduit means also connecting said supply means to said enclosure, means responsive to air flow through said conduit, and adjustable second means controlling said supply means in response to said air flow responsive means in a manner to supersede said first means and maintain said air flow above an adjustable predetermined value without regard to the air pressure required by said first means.

W'ILLIAM EVERT WELCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,508,707 Moss Sept. 16, 1924 1,508,731 Standerwick Sept. 16, 1924 1,969,350 Shackleton May 29, 1934 2,092,957 Gregg May 21, 1935 2,119,402 Puifer May 31, 1938 2,173,331 Haines Sept. 19, 1939 2,182,192 Becker Dec. 5, 1939 2,208,554 Erice July 16, 1940 2,265,461 Wagner Dec. 9, 1941 2,284,984 Nixon et al June 2, 1942 2,350,896 Joe June 6, 1944 2,353,201 Talbot July 11, 1944 2,371,732 Bristol Mar. 20, 1945 2,374,708 Shoults May 1, 1945 2,376,142 Hoffman et al May 15, 1945 2,377,199 Adams May 29, 1945 2,385,664 Warner e Sept. 25, 1945 2,425,607 Edwards et al Aug. 12, 1947 2,450,881 Cooper et al Oct. 12, 1948 2,451,835 Johnson Oct. 19, 1948 

